Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.49	8.385%	$90.4906	$90.49	$90.50	$90.50
Purchase #2	$180.99	3.698%	$187.683	$187.68	$187.70	$187.70
Purchase #3	$132.42	10.590%	$146.4433	$146.44	$146.45	$146.40
Purchase #4	$72.44	13.538%	$82.2469	$82.25	$82.25	$82.20
Purchase #5	$208.91	3.519%	$216.2615	$216.26	$216.25	$216.30
Purchase #6	$203.61	13.644%	$231.3905	$231.39	$231.40	$231.40
Purchase #7	$245.78	9.590%	$269.3503	$269.35	$269.35	$269.40
7 purchase totals =	$1,127.64		$1,223.8661	$1,223.86	$1,223.90	$1,223.90